1. Field of the Invention
The present invention relates to a device for digital data transmission with a U-shaped support rail and a plastic strand which can be clamped in a positively engaging manner into the U-shaped support rail. A strip-like metal contact conductor is mounted on a portion of the inner side of the plastic strand located frontally opposite and at a distance from an insertion gap for a collector shoe which is longitudinally movable in the support rail. The contact conductor contacts a contact body of the collector shoe. Compared to the plastic strand, the contract conductor has a significantly smaller thickness. A shielding member is provided between the inner side of the plastic strand and the support rail. In the area of the insertion gap, the shielding member has shield contact surfaces which interact with a contact piece of the collector shoe.
2. Description of the Related Art
A device of the above-described type is disclosed in German Patent 41 22 469. The device includes a plastic strand which, in the flat state thereof, has a thickness which is small as compared to its width. A narrow metal contact conductor is arranged on one side and in the middle of the plastic strand. The thickness of the contact conductor is significantly smaller than the thickness of the plastic strand. The plastic strand has on its other side a shielding member composed of a mesh. The shielding member engages in a clamp-like manner around the longitudinal edges of the plastic strand. Narrow shield contact surfaces for connecting the shielding member to ground through a mobile collector are provided on the outer sides of the short portions of the screening member engaging around the longitudinal edges of the plastic strand. Together with the contact conductor and the shielding member, the plastic strand is clamped into a U-shaped support rail of plastics material. For this purpose, the support rail has two sides which over the entire height thereof extend parallel to each other and which are connected to each other by a curved bight. The free ends of the sides are provided with clamping grooves which are open toward the bight and which are bordered on one side by adjacent low clamping groove walls. The clamping grooves serve to secure the plastics strand in a clamping manner and for shielding. The distance of the contact conductor from the opening of the insertion gap between the ends of the sides of the support rail is a multiple of the width of the insertion gap. The width of the insertion gap also essentially corresponds to the depth of the insertion gap.
Even though the known device has been found useful, it has been found particularly in practical use that the device has properties which can be improved. Improvements are especially required in the manner in which the contact conductor is secured to the inner side of the plastic strand, in the arrangement of the shielding member between the inner side of the plastic strand and the support rail, and in the positions of the shield contact surfaces without and with contact by the mobile collector.